There is a stair of 10 steps.IF you can only go up for 1 steps or 2 steps once.How many ways can

题目

There is a stair of 10 steps.IF you can only go up for 1 steps or 2 steps once.How many ways can
you use to get to the 10th step?

答案

2+2+2+2+2 一种方法2+2+2+2+1+1 6!/(4!x2!)=15种2+2+2+1+1+1+1 7!/(3!x4!)=35种2+2+6个1 8!/(2!x6!)=28种2+8个1 9!/8!=9种10个1 一种方法一共1+15+35+28+9+1=89种方法...